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New Horizons Jupiter Encounter
ugordan
post Jan 26 2007, 06:45 PM
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Here's the comparison between LORRI and ISS NA I promised. It shows Ganymede from lor_0031303982_0x630_sci_1.jpg. I used a Cassini frame (N1351684677_2.IMG) of approximately the same pixel scale, meaning taken from a distance of 56.7 mil. km as opposed to 68 mil. km due to LORRI's smaller FOV (0.29 vs 0.35 deg). Unfortunately there was no clear-filtered image at around this time so I used a GRN filter for Cassini. This might give a slightly sharper image than the entire passband would. The JPG artifacting is IMHO negligible in the NH image. The middle set was "sensibly" sharpened to bring out most details without producing strong edge ringing. Magnified 4x. The two views probably show opposing hemispheres so no similar features are visible.



Comparing ISS NAC with its 30.5 kilogram mass and peak power of 26 W to LORRI really shows the latter's sure one capable camera, even if having a slightly fuzzier image! Not to mention sensitivity, 3 ms exposures are more typical of what Cassini's WAC used at Jupiter, NAC used several tens of ms.

EDIT: Added simulated views using Solar System Simulator to show rough albedo features.


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Planet X
post Jan 26 2007, 09:05 PM
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QUOTE (J.J. @ Jan 25 2007, 05:41 PM) *
Based on the approximate orbital velocity of Pluto at encounter, and the total relative velocity of NH and Pluto at encounter, I (awhile back) derived a velocity of ~12.7 km/s for NH at Pluto. Assuming that's correct, that puts NH well above the velocities of P10 and P11 (at 12.1 and 11.5 km/s, respectively), but far below either of the Voyagers (at 15.6 km/s for V2 and 17.1 km/s for V1).

For those a little more bored than I, one can calculate the "loss distance" of NH from P10 and P11, based on the difference in velocities. Lessee...NH will be moving at about 2.7 AU/yr. once she passes Pluto. That means she'll be gaining 1.2 AU/yr. relative to P11, and 0.6 AU/yr. relative to P10. That isn't as much as it sounds; if my numbers are right, NH won't catch up with P11 until ~2066 (at 138 AU), and not to P10 until ~2151 (at 367 AU).

For the record, in 2066, the Voyagers will be at:

V2: 250 AU
V1: 286 AU

In 2151:

V2: 531 AU
V1: 592 AU

Feel free to check my figures, all.


Those figures are a bit off I'd say. I think you've mistakenly thought that 0.1 km/s is equivilant to 0.1 AU/yr. A speed of 0.1 km/s actually equals 360 km/hr, or 3153600 km (~0.02 AU) per year. A speed of 1.0 km/s, therefore, equals ~0.2 AU/yr.

That said, NH will actually be moving at ~14 km/s relative to the sun at the time of Pluto encounter. However, I read awhile back that NH will reach 100 AU in December 2038 after traveling at an average speed of ~13 km/s during a cruise of over 23 years from Pluto to 100 AU. This means that NH's speed will have slowed down from ~14km/s at the Pluto encounter to ~12 km/s at the 100 AU crossing. Interestingly enough, the speed of Pioneer 10 at 100 AU is also ~12km/s!

If this is indeed correct, then NH may not even catch Pioneer 10! It will still easily whup Pioneer 11, though, as that spacecraft will have slowed down to ~2.3 AU/yr when it reaches 100 AU in late January 2019. Later!

J P
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helvick
post Jan 27 2007, 01:49 PM
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QUOTE (elakdawalla @ Jan 26 2007, 05:36 PM) *
Why would the FWHM be wider through the clear filters than the IR? huh.gif

Chromatic aberration would seem logical to me.
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ugordan
post Jan 27 2007, 04:59 PM
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Cassini NAC is a reflector telescope and I don't see any obvious refracting elements in its design (such as field flattening optics) so where would chromatic aberration come from? Maybe the design simply optimizes for focus using the IR filters (they do, after all affect focus ever-so-slightly) so using no filter (clear frame) produces a slight defocus. Diffraction/wavelength effects would make longer wavelengths more blurred, contrary to this behaviour, right?
I know the WAC uses a special "clear" filter that improves focus over the visible wavelengths since it's basically an old Voyager WAC optics design.

EDIT: Correction, there appear to be field corrector optics and the window of the CCD package in the NAC. Chromatic aberration might be the sole reason for the PSF variation.

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Back on topic... A question for John or Alan: What are the maximum exposures for LORRI without saturating various targets at Jupiter, at these approach phase angles? I see a typical exposure is 3 ms. The difference between 4 ms and 2 ms seems to be quite a bit less noise in the former case. Is the only reason such low exposures are used to avoid overexposure (say at Europa / Io)?

This post has been edited by ugordan: Jan 27 2007, 08:22 PM


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yaohua2000
post Jan 29 2007, 05:38 AM
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New Horizons was 50 million kilometers away from Jupiter at 2007-01-28 13:09:38 UTC.
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Guest_AlexBlackwell_*
post Jan 29 2007, 07:49 PM
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Guests






Planetary Radio
NEW HORIZONS APPROACHES JUPITER!
Airdate: Monday, January 29, 2007
http://planetary.org/radio/show/00000221/
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Bjorn Jonsson
post Jan 29 2007, 08:17 PM
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For comparison purposes I did a a montage of global images from all of the spacecraft that have flown by Jupiter and imaged it (Galileo is omitted because there is no low phase global coverage):

Attached Image


The northern hemisphere is very similar in the NH and Voyager images. There are differences but some of these may be due to LORRI's greater wavelength coverage.

The southern hemisphere is somewhat similar to its appearance in the Cassini images with the biggest visible difference being that the region around the Great Red Spot appears far less turbulent. The GRS itself is noticeable smaller in longitudinal extent than it was during the Voyager flybys.

EDIT: The Cassini and Voyager images are calibrated green filtered images without any further processing. No clear-filter images were available. The Pioneer images are scanned color images I converted to grayscale and contrast enhanced slightly.
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elakdawalla
post Jan 29 2007, 08:45 PM
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Cool montage, Bjorn!

Are these all clear-filter images? Are there differences in these images attributable to what bandpasses the cameras were sensitive to?

--Emily


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Bjorn Jonsson
post Jan 29 2007, 10:18 PM
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I forgot to specify the filters - they have been added into my original message.

The different filters account for some of the differences but the effect is probably minor. I have found that clear-filter images are more similar to green-filter images than to red and blue images. This is especially true of red features like the GRS.
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Toma B
post Jan 30 2007, 07:22 AM
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There has been an update on the "New Horizons Science Operations Center" OR NOT?!?! blink.gif
I really don't know...now...
This morning I opened that page and I saw some new images (more than 10) taken on 24th January ,saved it than clicked "BACK" and there was no new images anymore including the one that I just saved...
I tried everything that I know to get that new images page back but it's just gone!!!

Maybe I'm imagining things or dreamed it but there are now 56 images of Jupiter on "New Horizons SOC"
and I have 57 on my HDD...!?!

Here is that extra image I'm talking about:

Attached Image


Have you seen this image yet?


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My "Astrophotos" gallery on flickr...
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Ian R
post Jan 30 2007, 09:34 AM
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Is this a rogue pixel, or one of the smaller, inner moons? unsure.gif

Attached Image


Ian.


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ugordan
post Jan 30 2007, 09:45 AM
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Noise. NH is still too far out to resolve anything except the Galileans. If that were a real feature, it would be slightly smudged over more than 1 pixel due to the point spread function.


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djellison
post Jan 30 2007, 09:54 AM
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http://space.jpl.nasa.gov/cgi-bin/wspace?t...=1&showsc=1

The view at the time of the picture ( roughly )

Doug
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Alan Stern
post Jan 30 2007, 12:47 PM
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Toma B-- More images will be posted as they are received. The SOC description page is under development and is planned for permanent posting this week.

-Alan
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JRehling
post Jan 30 2007, 06:51 PM
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QUOTE (Bjorn Jonsson @ Jan 29 2007, 02:18 PM) *
I forgot to specify the filters - they have been added into my original message.

The different filters account for some of the differences but the effect is probably minor. I have found that clear-filter images are more similar to green-filter images than to red and blue images. This is especially true of red features like the GRS.


In principle, this would depend upon the sensitivity of the photosensitive substrate, which can vary for two cameras with the same (clear or otherwise) filter.

I wonder if the Pioneer cameras were intrinsically more sensitive to blues, making the GRS stand out as a much darker feature than in Voyager, etc. images. Alternately, the GRS may have changes in the intervening few years. Given the fact that all features appear to be a bit different in Pioneer vs. Voyager images, I suspect that this is a case of what's behind the clear filters not being the same.
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